Process of tin plating



'following description.

.pearing surfaces of lacquered cans and contain- Pnt ented May 14, 1935 UNITED STATES PATENT OFFICE j PROCESS OF TIN PLATING Francis 1!. Snyder, Niagara Falls, N. Y., and Stanley F. M. Maclaren, Niagara Falls, Ontario, Canada, assignors to Industrial Research, Limited, Niagara Falls, Ontario, Canada, a corporation of Ontario No Drawing. ApplicationNovember 10, 1931,

Serial N0. 574,226

' 3 Claims. (01. ill-70.2)

This invention relates to an improved tin purpose. Thereafter the sheets are washed plating process and more particularly to an thoroughly with water and are promptly 1mimproved process of coating light gauge sheet mersed in a suitable solution, such as zinc chlometal, such as thin sheet iron, with a corroride, to prevent the action of the air or other sion resisting tin-cadmium alloy. oxidizing agent thereon.

The principal object of the present invention The pickled and washed sheets are plated by is to provide an improved process of coating thin dipping them in a molten mass of a, tin-cadmium gauge sheet metal for use in the manufacture of alloy. In preferred practicethe alloy consists of so-called tin cans. 90 per cent. tin and 10 per cent. cadmium by An important object of the invention is to weight. The cadmium content may be varied provide thin gauge ironsheets plated with a from about 1 per cent. to approximately per corrosion resisting tin-containing alloy which cent. but we have found that there is no pracare bright and attractive in appearance and tical advantage in employing substantially more which are particularly adapted to be fabricated than 10'per cent. cadmium and that the results into containers in which foods may be safely of the plating are somewhat less satisfactory as packed without further coating of the metal the cadmium content approaches 1 per cent. In as with lacquer or the like. the preferred operation of'the process the tem Other objects and advantages of the invention perature of the molten mass is maintained will become apparent during the course of the around 220 C. although this temperature may be varied considerably. Obviously the temperature must be suflicient to. maintain the mass in molten condition during the period of treatment butthe use of a temperature substantially in excess of 220 0., while practical in some instances, is disadvantageous in that excessive splashing of the molten metal results. Moreover, too thin a film of alloy is deposited when a temperature substantially in excess of the pre- As is well known, it is customary practice in the manufacture of so-called tin cans and tin containers in which articles of food are to be packed to apply to the interior surfaces of the cans or containers a protective coating such as a lacquer in order to prevent the formation of deleterious ingredients in the food as a result of the reaction between compounds present in the food with the metal from which the cans and ferred temperature is employed. containers are made. This practice of lacquering In order to reduce the possibility of oxidation the interiors of such containers was necessitated during the treatment it is advisable to add to primarily by the fact that the processes 'customthe molten metal a flux which has a melting arily used in plating thin guage sheet metal point below the operating temperature of the were not successful in entirely covering the base process. Various fluxes may be employed but metal. For example, the ordinary tin containers we recommend the use of a flux consisting of in general commercial use will often contain soper cent. zinc chloride, 15 per cent. sodium called pinholes as a result of the imperfect covchloride and 5 per cent. potassium chloride, the ering of the base metal with the tin coating. percentages being calculated inparts by weight.

Although there has been' somewhat of an un The time of treatment of the metal sheets in favorable reaction by the public to the dark apthe molten mass may be varied considerably depending upon the temperature of operation, the alloy used and the thickness of the coating desired. Where, as in the preferred practice, an alloy of per cent. tin and 10 per cent. cadmium is employed with a flux of the type referred to above and the process is operated at a temperature of about 220 C. it is necessary to immerse the sheets in the molten bath for only about two or three minutes. Following the coating of the sheets in the molten bath they are wiped to the so desired thinness of film according to conventional practice. Thereupon the sheets are quenched with water in conventional manner, after which the sheets are ready for use as desired.

As indicated above the treatment described im- 55 ers manufacturers have been unwilling to dis continue the lacquering process because of the possible dangers to health resulting from packing certain fruits and meat products in unlacquered containers. By the use of the present invention the use of lacquers and similar pro-' tective coatings may be safely eliminated thereby saving the expense of the separate lacquering process as well as providing cans and containers having bright, attractive surfaces.

In the practice of the present invention the sheets of thin guage iron to be plated are first given'a fast bright pickle according to any of the usual pickling processes now employed for this products therein. One of the most important advantages of the process is that the plated metal produced is entirely inert with respect to fruit .acids and other constituents in food products which are customarily packed in tin containers with the result that it is wholly unnecessary to apply to the inner surfaces of containers made from metal prepared in accordance with the present process an additional coating of lacquer or the like.

While we have described in detail the preferred practice of our invention, it is to be understood that the details of procedure may be variously modified without departing from the spirit of the invention or the scope of the subjoined claims.

We claim:

1. The process of manufacturing plated light guage metal sheets to be used in'the manufacture of cans and the like which comprises cleaning the surface of the metal sheet under treatment, and applying a corrosion resisting coating to the cleaned sheet by immersing the same in a molten bath of an alloy consisting of approximately 10 per cent. cadmium and 90 per cent. tin.

- 2. The process oi! manufacturing plated light guage iron sheets to be used in the manufacture of cans and the like which comprises subjecting the iron sheets to a fast bright pickle, and subsequently applying a corrosion resisting coating to the sheets by immersing the same for approximately two or three minutes in a molten bath of an alloy consisting of approximately 10 per cent. cadmium and 90 per cent. tin, said bath being maintained at a temperature of approximately 220 C. during the treatment, removing the sheets from the bath, wiping the sheets to provide a metal film of the desired degree of thickness, and

quenching the thus treated sheets in water.

3. The process of manufacturing plated light guage metal sheets to be used in the manufacture of cans and the like which comprises cleaning the surface of the metal sheet under treatment, and applying a metal coating to the cleaned sheet by immersing the same in a molten bath of an alloy consisting of cadmium and tin, the cadmium constituting approximately from 1 to .10 per cent. by weight of said alloy.

FRANCIS H. SNYDER.

STANLEY F. M. MACLAREN. 

